1. Field of the Invention
This invention relates to a safe, convenient and economical method for chlorinating pendant methyl groups of methyl vinyl aromatic polymers. More specifically, this invention relates to the phase transfer catalyzed chlorination of poly(p-methylstyrene).
2. Brief Description of the Prior Art
Chloromethylated polystyrenes are known as intermediates in the preparation and manufacture of ion exchange resins, supports for solid phase peptide synthesis, and supports for polymeric reagents and catalysts. Prior to the present invention, several methods of introducing the chloromethyl groups into polystyrenes have been proposed and employed with each method exhibiting serious problems and/or severe limitations. Lewis acid-catalyzed direct chloromethylation of a vinyl aromatic polymer represents the most prevalent commercial route of synthesis but requires the use of carcinogenic chloromethyl methyl ether and its unavoidable contaminant, the far more potent carcinogen bis(chloromethyl)ether. Methods of generating chloromethyl methyl ether in situ and alternate less volatile chloromethyl ethers of unknown toxicity have been proposed to lessen the hazard. Polymerization of vinyl benzyl chloride or other chloromethyl-substituted vinyl aromatic monomer (e.g., the copolymerization of chloromethyl styrenes available as a 70/30 m/p mixture) represents an alternative route to the production of chloromethylsubstituted polystyrenes. However, the chloromethylsubstituted vinyl aromatic monomers are expensive to produce and consequently, the method is seldom used. Another known method is disclosed in U. S. Pat. No. 3,812,061 wherein the chlorination of vinyl aromatic polymers having pendant methyl groups (e.g., cross-linked poly(vinyltoluene)), is achieved by the reaction of sulfuryl chloride in the presence of a free radical catalyst. However, sulfuryl chloride is a highly toxic and corrosive lachrymator.